Ethernet has long been an established standard technology in office communication. Ethernet is now being used for new applications in industrial controls and in substation automation. Ethernet has also found use in the automotive industry for diagnostic access and has been explored for further usage in vehicular applications.
Embedded Ethernet MACs and switches are utilized to provide Ethernet network connectivity to a host processor. The host processor may typically perform any number of functions such as, for example: device functions such as capturing sensor data from various sensors such as temperature sensor, accelerometer sensors, and position sensors; actuator functions such as controlling synchro motors, linear actuators, solenoids and valves; hybrid functions such as combination sensor and actuator functions; human-machine interface functions; data recorder functions; and gateway functions such as connecting multiple sensors and actuators via another communication means. Host functions may also include controller functions to control various devices and sensors; supervisory functions used for setup and maintenance of other elements on the network; and standalone subsystem functions.
The use of two-port switches in industrial networking is typical for one of two primary reasons, although they can coincide. A first reason is for providing daisy chain and ring networking topologies. Daisy chain networking reduces cabling and installation costs in many cases, eliminates dedicated infrastructure switch devices, provides a familiar installation approach, and requires a reduced cabinet footprint, i.e., a reduced infrastructure switch count. A second reason is redundancy. With appropriate network management protocols in a ring topology, the two-port switches provide no loss of functionality on a single point of failure in the network.
Specialized protocols that run on top of standard Ethernet also require a daisy-chain or ring topologies as a basic part of their operation. Such protocols include: PROFINET IRT (class C), Sercos III, EtherNet/IP DLR, HSR (a ring-redundancy protocol related to substation automation), and ETHERCAT. PRP, another redundancy protocol related to substation automation, requires two ports, but not operating as a switch.